Multiple unit tube



Filed July 31. 1928 INVENTOR WALTER AKEMANN ORNEY Patented Apr. 10, 1934 PATENT OFFICE MULTIPLE UNIT TUBE Walter Akemann, Dahlem, near Berlin, Germany,

asslgnor to Allgemeine Elektrizitats-Gesellschaft, Berlin, Germany, a corporation of Germany Application July 31, 1928, Serial No. 296,431 In Germany August 9, 1927 4 Claims.

This invention relates to a multiple unit tube having alternating current operated cathode.

In the case of alternating current heated fila- :ments, line noises transferred from the filament to the grid play a serious part, and are extremely objectionable, especially in the case of multipleunit tubes for, because of their compact construction the line variations are readily amplified and rendered audible.

These disadvantages, according to the present invention are obviated by utilizing indirect alternating current heating, in other words, by heating an electron-emissive film or layer indirectly so that the emissive coat thus has no connection, that is, is electrically independent from the parts carrying the line or supply current. The said inconvenience, especially in multiple-unit tubes is further obviated, according to this invention,

-by choosing the filament current carrying parts so short that capacitive coupling between the filament leads and other parts of the receiver set, especially the grid leads, are reduced to a minimum. In this way the screening or shielding of the filament leads, which is otherwise required,

can be dispensed with. By the adoption of both these preventive means, the disturbing action of line noises is minimized.

In the drawing, a circuit diagram for a multiple-unit tube embodying these features is shown.

This tube is characterized by the above mentioned features that (1)' the cathodes which comprise as shown an electron emissive layer C indirectly heated by the heater elements H are indirectly fed with alternating current, that is to say, the active or emissive films C of the cathodes are united only with point K, a junction point of the plate battery B, but not with the leads R carrying the current supplied from the network, and that (2) the supply of the alternating current for heating the different cathodes C is effected inside the tube over the shortest possible path as shown so that the capacitive couplings between these leads R and the grid circuits are reduced to a minimum value. This has the result that no special shielding of these wires will be necessary.

Referring more particularly to the drawing, the evacuated envelope E contains a plurality of resistance coupled stages, each comprising the indi-- rectly heated cathode C, control grid G and plate P. The tunable input circuit I is connected on one side to the grid G of the first stage and on the other side to the common cathode terminal K through a portion 5 of the B battery arranged to bias said control grid. Each plate circuit of the first two stages contains a resistance 3, and each grid circuit of the second and third stages contains a leak resistance 2. A condenser 4 serves to couple the respective plate circuit of the first and second stages to the succeeding grid circuit. The portions 5 and 6 of the B battery serve to impress a greater negative biasing potential on the control grid of the last stage than that impressed on the grid of the first stage. The output or plate circuit of the third or last stage contains the indicating device 0, such as a telephone or loud speaker.

I claim as my invention:

1. A multiple unit tube-comprising a plurality of amplifying units, each comprising an indirectly heated cathode, a grid electrode, and a plate electrode, coupling circuits for connecting said units in cascade, and a sealed envelope enclosing said units and said circuits and having a single cathode terminal, a connection between said cathode terminal and one of the grid electrodes, and a separate terminal connected to each of the other grid electrodes for applying biasing potentials to said grid. electrodes.

2. A multiple unit discharge tube comprising a sealed envelope enclosing a plurality of amplifying units, each comprising a cathode having an electron emitting member and a heater adjacent and electrically independent of said member, a grid electrode, and a plate electrode, current supply leads of minimum length inside said envelope and to which said heaters are connected in parallel, separate terminals on said envelope one for each of said grid electrodes, and a connection inside said envelope between one of said grid terminals and all said electron emitting members, whereby said last mentioned electrodes are maintained at the same potential.

3. A multiple unit discharge tube comprising a sealed envelope enclosing a plurality of amplifying units, each comprising a plate electrode, a grid electrode, and a cathode having an oxide coated member and a heater adjacent and electrically independent of said members, a single terminal on said envelope connected to all of said oxide coated members and also to one of said grid electrodes, a separate terminal on said envelope for each of the other grid electrodes, coupling circuits within said envelope and between said units, and current supply leads of minimum length within said envelope, said heaters being connected in parallel to said supply leads.

4. A multiple unit discharge tube comprising a sealed envelope enclosing a plurality of resistrectly heated cathode, a grid electrode and a other grid electrodes, a third terminal on said envelope connected through a resistance to another of the grid electrodes, and additional terminals on the envelope connected to the several plate electrodes.

WALTER AKEMANN. 

